Content Standard 1: The student will analyze causes, key events, and effects of the Civil War / Reconstruction era.

In 1845 the United States annexed the Republic of Texas, which had recently won its independence from Mexico. Tension between the United States and Mexico mounted following a dispute over the location of the Texas border. This dispute led to the Mexican War (1846-1848). At the conclusion of the war, Mexico ceded a large tract of territory that composes much of what is now the southwestern United State.